Field of the Invention
This invention relates, in general, to sewing machines and, in particular, to a new and useful sewing group which is connectible to a feed guide for the purpose of effecting specific sewing operations.
The invention relates particularly to a sewing group such as is known through German patent No. 3,407,338 corresponding to U.S. Pat. No. 4,555,998. To achieve lower inertia, its feed device has only two rotatably mounted links, each mounted on a slide which is displaceable in a straight line and connected via a toothed belt drive to a positioning motor for each. At the end of one of the two links a work-holder is arranged. During operation there occur at the link carrying the work-holder, in addition to the drive forces directed parallel to the longitudinal axis of the link, additionally also bending loads due to perpendicularly directed forces at its coupling point with the other link. These bending loads are absorbed by the fact that the link carrying the work-holder has a rigid center rod and a transverse rod connected with the work-holder. The ends of the transverse rod are connected with the other end of the link through tensioned spring steel strips. These measures however, involve considerable engineering expense.
This arrangement of the work-holder at the end of one of two coupled links, known also in older feed devices composed of four links in parallelogram arrangement (German patent No. 2,457,534) corresponding to U.S. Pat. No. 4,073,252, results furthermore in unequal drive conditions for the two directions of movement of the feed device. Also, for the feed in longitudinal directions of the coupled link, much greater forces must be supplied than for the feed in longitudinal direction of the link carrying the work-holder. These unequal forces are mastered without a problem by the cam drives used in the older feed devices. In a feed device equipped with two step motors, on the contrary, great differences between the drive forces maximally to be supplied may necessitate both the use of different drive ramps for the operation of the step motors and also a disproportionately great reduction of the maximum speed of the motors.